Study objectives: To describe a technique for the use of methadone during and following lower abdominal surgery that integrates its pharmacokinetic and pharmacodynamic properties with the objective of postoperative analgesia; to compare methadone with morphine for postoperative pain control.
Design: Randomized prospective clinical trial. Patients were not told which agent they received (single-blind).
Setting: Department of anesthesia and gynecology surgical service at a university medical center.
Patients: Forty women undergoing abdominal hysterectomy (n = 39) or myomectomy (n = 1).
Interventions: Patients received either methadone (Group 1) or morphine (Group 2) 20 mg intravenously (IV) following induction of anesthesia, additional IV opioid in the recovery room, and subsequent opioid as needed (PRN) intramuscularly (IM) on the postsurgical wards.
Measurements and main results: Pain was assessed using a visual analog scale (VAS). Respiratory rate, sedation, and hemodynamics were assessed frequently (at least every 4 hours). Patients were studied for 72 hours following recovery room discharge. Patients required less methadone than morphine in the recovery room (2.0 +/- 2.9 mg vs 4.4 +/- 2.9 mg). Patients requested less methadone than morphine for pain relief on the wards (4.5 +/- 4.2 mg vs 42.3 +/- 14.3 mg). Patients in the methadone group reported lower pain intensity by VAS (1.9 +/- 0.3 vs 3.4 +/- 0.6). These differences are statistically significant (p less than 0.01).
Conclusion: Sustained analgesia with methadone is predicted by its pharmacokinetics. Patients who received 22 +/- 2.9 mg of IV methadone (combined intraoperative and recovery room doses) reported less pain and required minimal additional analgesic over the next 72 hours than did patients who received morphine. This is consistent with sustained therapeutic plasma levels due to methadone's long plasma half-life (54 +/- 20 hours). Use of methadone in this manner is an effective therapy for postoperative pain control and is not associated with toxicity or notable side effects.